Re: [PATCH] PM / devfreq: stopping the governor before device_unregister()
From: Chanwoo Choi <cw00.choi@samsung.com>
Date: 2018-08-31 08:52:49
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Hi, On 2018년 08월 30일 19:02, vincent.donnefort@arm.com wrote:
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From: Vincent Donnefort <redacted> device_release() is freeing the resources before calling the device specific release callback which is, in the case of devfreq, stopping the governor. It is a problem as some governors are using the device resources. e.g. simpleondemand which is using the devfreq deferrable monitoring work. If it is not stopped before the resources are freed, it might lead to a use after free. Signed-off-by: Vincent Donnefort <redacted> Reviewed-by: John Einar Reitan <redacted>diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c index 4c49bb1..4e43830 100644 --- a/drivers/devfreq/devfreq.c +++ b/drivers/devfreq/devfreq.c@@ -534,10 +534,6 @@ static void devfreq_dev_release(struct device *dev) list_del(&devfreq->node); mutex_unlock(&devfreq_list_lock); - if (devfreq->governor) - devfreq->governor->event_handler(devfreq, - DEVFREQ_GOV_STOP, NULL); - if (devfreq->profile->exit) devfreq->profile->exit(devfreq->dev.parent);@@ -672,7 +668,7 @@ struct devfreq *devfreq_add_device(struct device *dev, list_del(&devfreq->node); mutex_unlock(&devfreq_list_lock); - device_unregister(&devfreq->dev); + devfreq_remove_device(devfreq); devfreq = NULL; err_dev: if (devfreq)@@ -693,6 +689,9 @@ int devfreq_remove_device(struct devfreq *devfreq) if (!devfreq) return -EINVAL; + if (devfreq->governor) + devfreq->governor->event_handler(devfreq, + DEVFREQ_GOV_STOP, NULL); device_unregister(&devfreq->dev); return 0;
As description of this patch, if devfreq_wq is executed and then execute the 'devfreq->governor->get_target_freq' between step1 and step2 after already freed the 'dev' related resource, it might happen the problem because the registered callback of get_target_freq requires the 'dev' resource. device_unregister(dev) step 1. device_del(dev) <- if devfreq_wq is executed step 2. put_device(dev) device_release() devfreq_dev_release() stop the governor for specific devfreq instance It looks good to me. Stop the governor before calling device_unregister(). Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com> -- Best Regards, Chanwoo Choi Samsung Electronics